The present invention relates generally to the field of voltage regulators, and more particularly, to a linear regulator circuit and method.
Many direct current (DC) electronic devices, such as integrated circuits and microprocessors, require a constant voltage within certain tolerances. The task of providing this voltage is made difficult by the small fluctuations in a voltage generator, and by the variation in load current required by the DC device.
One type of circuit that can be used to provide a constant voltage is a linear regulator. A linear regulator may have a capacitor connected to its output terminal at which the output voltage appears. This capacitorxe2x80x94xe2x80x94which can be a discrete component, separate from the linear regulatorxe2x80x94xe2x80x94functions to stabilize the output voltage when the load current changes rapidly. The suitability of a certain capacitor for this application is governed by two characteristics: its capacitance value, and its equivalent series resistance (ESR) value. The capacitance is a measure of the amount of charge a capacitor can hold. The equivalent series resistance (ESR) value of a capacitor affects how current is supplied by the capacitor, and how quickly it can respond to variations in load current. In a linear regulator implemented according to previously developed techniques, it is desirable to have a capacitor with a high value of capacitance and a low value of ESR. Such capacitors, however, can be relatively large and expensive. This drives up the total cost for providing a constant voltage. It also causes more power to be consumed, and requires more physical space to implement.
The disadvantages of and problems associated with previously developed linear regulators have been substantially reduced or eliminated using the present invention.
According to one embodiment of the present invention, a linear regulator circuit includes an input terminal for receiving an input voltage and an output terminal for providing an output voltage. A pass device, coupled to the input terminal and the output terminal, generates an output current. A feedback circuit is coupled to the pass device and the output terminal. The feedback circuit increases the output voltage as the output current decreases and decreases the output voltage as the output current increases.
According to another embodiment of the present invention, a method for providing a regulated voltage includes: receiving an input voltage; generating an output voltage and an output current; increasing the output voltage as the output current decreases; and decreasing the output voltage as the output current increases.
According to yet another embodiment of the present invention, a linear regulator circuit includes an input terminal for receiving an input voltage and an output terminal for providing an output voltage. A current sensing device is connected to at least one of the input terminal and the output terminal. The current sensing device senses a current flowing in the linear regulator circuit. A gain amplifier generates a voltage proportionate to the current. An adder combines the output voltage and the voltage output by the gain amplifier. An error amplifier, which may be coupled to the adder and the pass device, causes an increase in the output voltage as the current decreases and causes a decrease in the output voltage as the current increases.